JP6652882B2 - Pressure detector - Google Patents

Description

  The present invention relates to a pressure detecting device, and more particularly to a pressure detecting device using a bimorph in which two piezoelectric sheets are bonded.

  A pressure sensor using a piezoelectric sheet is known as a device for detecting the amount of pressure applied to a touch panel (for example, see Patent Document 1). In the touch input device disclosed in Patent Literature 1, pressure-sensitive sensors are overlapped on a flat surface of a flexible touch panel so as to be in close contact with each other.

JP 05-61592 A

  As a piezoelectric material used for the piezoelectric sheet, there are lead zirconate titanate (PZT), polyvinylidene fluoride (PVDF) and a polymer thereof. However, since these typical piezoelectric materials have pyroelectricity, it has been difficult to accurately detect the pressing force.

  Therefore, the inventor of the present application has paid attention to adopting a so-called bimorph structure in which two piezoelectric sheets are bonded to each other with their polarization directions reversed in order to improve this problem. The bimorph structure mainly has a rectangular or circular bimorph composed of two upper and lower piezoelectric elements. Detection electrodes are provided on both sides of the piezoelectric element. The bimorph structure further includes a frame-shaped support member mounted around a lower surface of the bimorph.

  As another example, the bimorph structure has glass or another member as a protective material on the upper surface of the bimorph to improve the strength of the piezoelectric element (prevention of scratches and cracks). In this case, the edge of the lower surface of the glass is supported by the frame-shaped support member.

Hereinafter, the mechanism of detecting the pressing force by the bimorph structure will be described. When the upper and lower piezoelectric elements are bent by the pressing force acting on the central portion, stress σ _u and stress σ _l proportional to the pressing force are generated in the upper and lower two piezoelectric elements in the respective piezoelectric elements.
+ In a bimorph structure with glass attached, both stress σ _u and stress σ _l are tensile stresses. In this case, since the direction of the stress sigma _u from stress sigma _l increases, it has been proposed to measure the pressing force by using the difference.

However, the bimorph structure provided with glass has a problem that the detection sensitivity is low because the difference between the tensile stress σ _u and the tensile stress σ _l is small.

  An object of the present invention is to increase detection sensitivity in a pressure detection device having a bimorph and glass or another member as a pressing surface.

  Hereinafter, a plurality of modes will be described as means for solving the problems. These embodiments can be arbitrarily combined as needed.

  A pressure detecting device according to an aspect of the present invention is provided so as to close an opening of a housing having an opening and a support portion around the opening, and two piezoelectric sheets that generate electric charges by externally applied pressure. This is a device for detecting pressure by using. The pressure detecting device includes a sheet member, a first piezoelectric sheet, and a second piezoelectric sheet.

  The sheet member has a first surface on which pressure is applied, and a second surface on which a part or all of the edge is fixed and supported on the support by the adhesive layer.

  The first piezoelectric sheet is arranged at the center of the second surface of the sheet member. The first piezoelectric sheet is anisotropic having an axis having a large axis and an axis having a small axis in which the amount of charge generated with respect to elongation is orthogonal to each other.

  The second piezoelectric sheet is disposed opposite to the first piezoelectric sheet on the side opposite to the sheet member of the first piezoelectric sheet. The second piezoelectric sheet is anisotropic having two axes which are orthogonal to each other and have a large axis and a small axis where the amount of electric charge generated by elongation is large.

  The arrangement of the fixed portions at the edges has a symmetry of less than twice symmetry.

  The first piezoelectric sheet and the second piezoelectric sheet are arranged such that axes having a large charge amount are orthogonal to each other.

  Here, the term “two-fold symmetry or less” means that it does not include 2n-fold symmetry (n is an integer of 2 or more), and means, for example, that it is not 4-fold, 8-fold, or 16-fold. .

  Since the arrangement of the fixed portion of the edge portion has symmetry of less than twice symmetry, the first piezoelectric sheet and the second piezoelectric sheet have an axis and a tensile stress that generate a large tensile stress when bending together with the sheet member. There is a small axis.

  In this device, when the first surface of the sheet member is pressed, the sheet member bends while its edge is supported by another member, and as a result, the first piezoelectric sheet and the second piezoelectric sheet also bend. At this time, the first piezoelectric sheet and the second piezoelectric sheet differ from each other in a plan view in which the axis in which the amount of electric charge generated with respect to elongation is large and the axis in which the tensile stress is small and large are parallel to each other.

  Hereinafter, an example will be described. In the first piezoelectric sheet, the axis where the amount of electric charge generated with respect to elongation is large and the axis where the tensile stress is small are parallel to each other. (It is orthogonal to the axis of large tensile stress). In the second piezoelectric sheet, the axis where the amount of electric charge generated with respect to elongation is large and the axis where the tensile stress is large are parallel to each other (perpendicular to the axis where the tensile stress is small). Then, a relatively large output can be obtained by adding the amount of charge generated on the first piezoelectric sheet and the amount of charge generated on the second piezoelectric sheet in the calculation of the pressing force calculation. That is, the pressure detection sensitivity of the pressure detection device is increased.

  In addition, when the arrangement of the fixed portion at the edge is, for example, four-fold symmetric (for example, when it is a square), or when the first piezoelectric sheet and the second piezoelectric sheet do not have anisotropy, the pressing is performed. When these charge amounts are added in the calculation of the pressure calculation, a large output cannot be obtained.

  The fixed portion of the edge may have a pair of first sides extending in the first direction.

  The pair of first sides may be straight lines parallel to each other.

The sheet member is long in one direction in plan view,
The pair of first sides may be edges extending in the longitudinal direction.

  The fixed portion of the edge may have a pair of second sides connecting the ends of the pair of first sides.

  The second side may have lower rigidity than the first side.

  The ends of the pair of first sides are spaced apart from each other, and may be discontinuous.

  In the pressure detection device according to the present invention, the pressure detection sensitivity of the pressure detection device is increased.

FIG. 3 is a perspective view of an electronic device. Sectional drawing of the II-II cross section in FIG. The top view of glass. The top view of a 1st piezoelectric sheet. The top view of a 2nd piezoelectric sheet. Sectional drawing of a pressure detector. Sectional drawing of a pressure detector. FIG. 9 is a plan view of a support substrate according to a second embodiment. FIG. 11 is a plan view of a support substrate according to a third embodiment. FIG. 14 is a plan view of a support substrate according to a fourth embodiment. FIG. 15 is a plan view of a support substrate according to a fifth embodiment. FIG. 17 is a plan view of a support substrate according to a sixth embodiment. Sectional drawing of the pressure detector of 7th Embodiment.

1. First Embodiment (1) Outline of Pressure Detector A pressure detector 100 according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view of an electronic device. FIG. 2 is a sectional view taken along the line II-II in FIG. In the following description, the terms “orthogonal” and “parallel” allow an error range and a range in which the described effect can be obtained.

  The pressure detector 100 is a device for measuring the magnitude of a pressing force (load) when pressed by a finger or a pen. In the following description, the near side (upper side in FIG. 2) as viewed from the user during use is referred to as the “input surface side” of the pressure detector 100, and the far side (lower side in FIG. 2) as viewed from the user is the pressure. It is referred to as the “back side” of the detector 100.

  As shown in FIG. 1, the electronic device 110 mainly includes the housing 6 and the pressure detector 100. The housing 6 has a rectangular frame shape and is made of synthetic resin. The pressure detector 100 is housed in the housing 6.

  More specifically, the housing 6 has a concave portion 6a that opens in a rectangular shape toward the input surface side. The concave portion 6a is formed so as to have a step around the opening, and the step portion serves as a support portion 6b. The inner edge of the support portion 6b corresponds to the opening shape of the concave portion 6a, that is, is formed in a rectangular frame shape. The support portion 6b corresponds to an edge of a back surface 1b of the support substrate 1 described later, and has a structure for supporting a pressure acting on the support substrate 1. In the recess 6a, a support substrate 1 described later is accommodated in a first area closer to the input surface than the support 6b, and a main body of the pressure detector 100 is accommodated in a second area on the back side.

  In the concave portion 6a, the side surface of the first region is in contact with the support substrate 1 with a small gap, and the side surface of the second region is in contact with the main body of the pressure detector 100 with a small gap. A space 7 is provided between the bottom surface of the housing 6 and the main body of the pressure detector 100.

  The pressure detector 100 mainly includes a support substrate 1, a piezoelectric sheet 3, and a detection electrode 4. As a basic operation of the pressure detector 100, when the support substrate 1 is pressed, the pressure detector 100 bends, a tensile stress is applied to the piezoelectric sheet 3, and an electric charge is generated. When the two detection electrodes 4 detect the charges, the pressing force applied to the pressure detector 100 can be detected.

More specifically, the pressure detector 100 is provided so as to close the opening of the housing 6, and the support substrate 1, the adhesive layer 2, the first detection electrode 4 a, It has one piezoelectric sheet 3a, a second piezoelectric sheet 3b, and a second detection electrode 4b. Hereinafter, each configuration will be described. In the cross-sectional views of FIG. 2 and the like, the position and thickness of each layer are appropriately adjusted for convenience of description.
(2) Support Substrate The support substrate 1 will be described in detail with reference to FIG. FIG. 3 is a plan view of the support substrate.

  The support substrate 1 (an example of a sheet member) is a sheet-shaped member, and its edge is disposed on the support portion 6 b of the housing 6. It has an input surface 1a (first surface) of the pressure detector 100. The support substrate 1 has a back surface 1b (second surface) on the side opposite to the input surface 1a. The edge of the back surface 1b of the support substrate 1 is fixed by an adhesive 8 (an example of an adhesive layer) so as to be supported by the support portion 6b. A double-sided tape (an example of an adhesive layer) may be used instead of the adhesive.

  The support substrate 1 preferably has transparency, scratch resistance, stain resistance, and the like as a protective plate. Examples of the material of the support substrate 1 include general-purpose resins such as polyethylene terephthalate and acrylic resins, general-purpose engineering resins such as polyacetal resins and polycarbonate resins, super-engineering resins such as polysulfone resins and polyphenylene sulfide resins, and glass. There is.

  The thickness of the support substrate 1 is, for example, 0.4 mm to 1.0 mm.

The support substrate 1 is rectangular as shown in FIG. 3, and all sides are fixed to the housing 6 with an adhesive 8. Therefore, the condition that “the arrangement of the fixed portion of the edge portion has symmetry of two-fold symmetry or less” is satisfied. Here, rotational symmetry is a group of symmetries that characterize a figure. When n is an integer of 2 or more, the property of overlapping with itself when rotated about a certain center by (360 / n) degrees is called n-fold symmetry. The term “two-fold symmetry or less” does not include 2n-fold symmetry (n is an integer of 2 or more), and means, for example, that it is not 4-fold, 8-fold, or 16-fold.
(3) Piezoelectric sheet The piezoelectric sheet will be described in detail with reference to FIGS. FIG. 4 is a plan view of the first piezoelectric sheet. FIG. 5 is a plan view of the second piezoelectric sheet.

  The piezoelectric sheet 3 is fixed to the back surface 1 b of the support substrate 1 via the adhesive layer 2. Note that the piezoelectric sheet 3 is disposed at the center of the back surface 1b of the support substrate 1.

  For the adhesive layer 2, for example, a transparent optical adhesive is used. One such example is Pressure Sensitive Adhesive (hereinafter "PSA"). The thickness A of the adhesive layer 2 is 5 μm to 300 μm.

  The elastic modulus of the adhesive layer 2 is not limited, but is about 10 MPa, preferably about 10 MPa or more and about 1 GPa. The material of the adhesive layer 2 is, for example, an acrylic, silicone, or epoxy adhesive. The adhesive layer 2 is preferably cured by UV curing or heat curing after bonding the adhesive.

  The piezoelectric sheet 3 is a sheet that generates a potential difference according to the pressing force applied to both surfaces when a bending force is applied. The piezoelectric sheet 3 is a serial bimorph composed of a first piezoelectric sheet 3a and a second piezoelectric sheet 3b. Both sheets have the same shape and face each other. The first piezoelectric sheet 3a is disposed on the back surface 1b side of the support substrate 1, and the second piezoelectric sheet 3b is disposed on the back surface side of the first piezoelectric sheet 3a (the opposite side of the first piezoelectric sheet 3a from the support substrate 1). 3a. The first piezoelectric sheet 3a and the second piezoelectric sheet 3b are bonded to each other by, for example, PSA.

As described above, since the support substrate 1 satisfies the condition that the arrangement of the fixed portion of the edge has symmetry of two-fold or less, as shown in FIGS. The first piezoelectric sheet 3a and the second piezoelectric sheet 3b have a first axis where a large tensile stress F1 is generated when bending together with the support substrate 1, and a second axis where a small tensile stress F2 is generated. The first axis extends parallel to the direction in which the rectangular short side 3A extends. The second axis extends parallel to the direction in which the long side 3B of the rectangle extends.
(4) Detection electrode The detection electrode 4 includes a first detection electrode 4a and a second detection electrode 4b. The first detection electrode 4a is disposed between the support substrate 1 (specifically, the adhesive layer 2) and the first piezoelectric sheet 3a (that is, on the side of the first piezoelectric sheet 3a opposite to the second piezoelectric sheet 3b). The second detection electrode 4b is arranged on the back side of the first piezoelectric sheet 3a (that is, on the opposite side of the second piezoelectric sheet 3b from the first piezoelectric sheet 3a).

  The first detection electrode 4a is connected to the ground. The second detection electrode 4b is connected to a detection circuit 53 described later.

  The first detection electrode 4a and the second detection electrode 4b are made of a conductive material. Examples of the conductive material include transparent conductive oxides such as indium-tin oxide (Indium-Tin-Oxide, ITO) and tin-zinc oxide (Tin-Zinc-Oxide, TZO), and polyethylene dioxythiophene. (Polyethylenedioxythiophene, PEDOT) and the like can be used. In this embodiment, the detection electrode 4 is formed directly on the surface of the piezoelectric sheet 3 using, for example, vapor deposition or screen printing.

  Note that the thickness of the detection electrode 4 can be, for example, 1 nm to 30,000 nm.

  Alternatively, a conductive metal such as copper or silver may be used as the conductive material. In this case, the detection electrode may be formed on the piezoelectric sheet by vapor deposition, or may be formed using a metal paste such as a copper paste or a silver paste. In addition, the detection electrode made of metal may have a mesh structure in order to improve translucency.

  The detection electrode may be formed on the surface of a resin film or the like by vapor deposition or screen printing, and may be fixed to a support substrate or a piezoelectric sheet with an adhesive.

Further, as the conductive material, a material in which a conductive material such as carbon nanotubes, metal particles, and metal nanofibers are dispersed in a binder may be used.
(5) Detector The second detection electrode 4b is connected to the charge amplifier 51 as shown in FIG. The charge amplifier 51 is connected to the detection circuit 53. The detection circuit 53 is a device that detects a pressing amount from a voltage signal detected by the detection electrode 4. The detection circuit 53 has, for example, an A / D converter and a pressing force calculation circuit.

With the above-described circuit configuration, the detection circuit 53 determines the amount of electric charge generated in the first piezoelectric sheet 3a (positively large in this embodiment) and the amount of electric charge generated in the second piezoelectric sheet 3b (negative in this embodiment). (Small) can be obtained.
(6) Pressing Means The pressing means for applying pressure to the pressure detector 100 is not particularly limited as long as it can apply pressure. Examples of the pressing means include a finger and a stylus ben.
(7) Detailed Description of Piezoelectric Sheet As the material of the first piezoelectric sheet 3a and the second piezoelectric sheet 3b, a sheet obtained by forming a ferroelectric material into a sheet shape and then polarizing it in the thickness direction can be used. Ferroelectric materials include PVDF, PVDF and copolymers such as TrFE and ETFE, and PZT. The first piezoelectric sheet 3a and the second piezoelectric sheet 3b are stacked such that the polarization directions are inverted upside down.

  Each of the first piezoelectric sheet 3a and the second piezoelectric sheet 3b is a piezoelectric body having anisotropy of physical properties by stretching, and is specifically made of, for example, a uniaxially stretched polyvinylidene fluoride film. The piezoelectric constant indicating polarization in the z-axis direction when stress or strain is applied in the x-axis direction of the uniaxial stretching direction is d31, and the piezoelectric constant in the z-axis direction when stress or strain is applied in the y-axis direction orthogonal to the x-axis. The piezoelectric constant indicating polarization is d32. In this case, in a piezoelectric body formed by uniaxial stretching of polyvinylidene fluoride, d31 is about twice or more than d32.

  In addition, the anisotropy of the physical property by stretching is also realized by providing a stretching difference in multiaxial stretching.

  As shown in FIG. 4, in the first piezoelectric sheet 3a, d31 is parallel to the direction in which the long side 3B of the rectangle extends, and d32 is parallel to the direction in which the short side 3A of the rectangle extends.

  As shown in FIG. 5, in the second piezoelectric sheet 31b, d31 is parallel to the direction in which the rectangular short side 3A extends, and d32 is parallel to the direction in which the rectangular long side 3B extends.

  As described above, the first piezoelectric sheet 3a and the second piezoelectric sheet 3b are arranged such that d31 are orthogonal to each other.

  Further, as shown in FIG. 4, in the first piezoelectric sheet 3a, the direction in which the above-described tensile stress F1 is generated is orthogonal to the direction of d31. As shown in FIG. 5, in the second piezoelectric sheet 3b, the direction in which the aforementioned tensile stress F1 occurs and the direction of d31 are parallel.

  The combination of the materials of the first piezoelectric sheet 3a and the second piezoelectric sheet 3b is not particularly limited. However, it is preferable that materials having the same characteristics are used for both sheets. This is because the output from the piezoelectric sheet caused by the thermal stress due to the temperature change and the pyroelectric effect can be canceled.

  A mechanism for canceling an output due to a pyroelectric effect in the piezoelectric sheet will be described with reference to FIG. FIG. 6 is a sectional view of the pressure detector.

  The first piezoelectric sheet 3a and the second piezoelectric sheet 3b are formed of a ferroelectric material, and the first piezoelectric sheet 3a and the second piezoelectric sheet 3b are configured such that the polarization directions in the non-pressed state are opposite to each other. If the temperature change occurs in the pressure detector 100 and a pyroelectric effect occurs in the piezoelectric sheet 3 as shown in FIG. 6, the input surface of the first piezoelectric sheet 3a and the second The same positive and negative charges are generated on the back side of the piezoelectric sheet 3b.

  When the first piezoelectric sheet 3a and the second piezoelectric sheet 3b are sufficiently thin (for example, 5 μm to 50 μm) and are made of a material having the same characteristics, the back surface of the first piezoelectric sheet 3a and the second piezoelectric sheet The potentials are substantially equal between the input surface of the sheet 3b and the input surface of the sheet 3b. As a result, between the input surface of the first piezoelectric sheet 3a and the rear surface of the second piezoelectric sheet 3b, It is derived that the potentials are equal.

  Therefore, with the above configuration, when the piezoelectric sheet 3 is affected by the pyroelectric effect, the potential on the input surface side of the first piezoelectric sheet 3a generated due to the pyroelectric effect and the second piezoelectric sheet The potential on the back surface of 3b is substantially equal. Then, in the pressure detector 100, when the first piezoelectric sheet 3a and the second piezoelectric sheet 3b are affected by the pyroelectric effect, the potential difference due to the pyroelectric effect as the piezoelectric sheet 3 detected by the detection electrode 4 is: , Almost “0”. Therefore, even if a pyroelectric effect occurs in the first piezoelectric sheet 3a and the second piezoelectric sheet 3b, almost no potential difference due to the pyroelectric effect is detected in the piezoelectric sheet 3 as a whole. That is, when the piezoelectric sheet 3 (the first piezoelectric sheet 3a and the second piezoelectric sheet 3b) is made of a ferroelectric material, the piezoelectric sheet 3 and the detection electrode 4 are configured as described above, so that a temperature change is prevented. Subsequent malfunctions (especially malfunctions caused by the pyroelectric effect) hardly occur.

  The charge generation mechanism when pressure is applied to the pressure detector 100 will be described with reference to FIG. FIG. 7 is a sectional view of the pressure detector.

When pressure is applied to the pressure detector 100, the support substrate 1 has higher rigidity than the piezoelectric sheet 3 and the detection electrode 4, and therefore, the piezoelectric sheet 3 (the first piezoelectric sheet 3a and the second piezoelectric sheet 3b) Generates tensile stress. At this time, a tensile stress σ _u is generated in the first piezoelectric sheet 3a, and a tensile stress σ _l is generated in the second piezoelectric sheet 3b. As a result, electric charges corresponding to the tensile stress are generated on the input-side surface and the back-side surface of the first piezoelectric sheet 3a and the second piezoelectric sheet 3b, respectively.

  In the pressure detector 100, when the input surface 1a of the support substrate 1 is pressed, the support substrate 1 bends while its edge is supported by the housing 6. As a result, the first piezoelectric sheet 3a and the second piezoelectric sheet 3b also bend.

  At this time, in the first piezoelectric sheet 3a and the second piezoelectric sheet 3b, the combination of the direction of d31 and the direction of d32 and the direction of the tensile stress F1 and the direction of the tensile stress F2 are different from each other in plan view. For example, in the first piezoelectric sheet 3a, as shown in FIG. 4, the direction of d31 is parallel to the direction of the tensile stress F2 (perpendicular to the direction of the tensile stress F1). In the second piezoelectric sheet 3b, as shown in FIG. 5, the direction of d31 is parallel to the direction of the tensile stress F1 (perpendicular to the direction of the tensile stress F2). Then, the detection circuit 53 adds these charge amounts in the calculation of the pressing force calculation, so that a relatively large output can be obtained. That is, the pressure detection sensitivity of the pressure detector 100 increases.

The planar shape of the fixed portion of the edge portion is, for example, four-fold symmetric (for example, the shape of the support substrate is square and the fixed portion has all four sides), or the first piezoelectric sheet 3a and the first If the piezoelectric sheet 3b does not have anisotropy, a large output cannot be obtained when these charge amounts are added in the calculation of the pressing force.
2. Second Embodiment A modification of the support substrate 1 will be described with reference to FIG. FIG. 8 is a plan view of a support substrate according to the second embodiment.

  As shown in FIG. 8, the support substrate 1A is square, and only two opposing sides 21 are fixed to a housing (not shown) by the adhesive 8.

  The first and second piezoelectric sheets (not shown) are also square.

  As described above, in this embodiment, the planar shape of the shape of the support substrate 1A is four-fold symmetric, but the condition that “the arrangement of the fixed portion of the edge has less than two-fold symmetry” is satisfied. As a result, the first piezoelectric sheet and the second piezoelectric sheet (not shown) have a first axis where a large tensile stress F1 is generated when bending together with the support substrate 1, and a second axis where a small tensile stress F2 is generated. There are two axes. The first axis extends in parallel with the direction in which the two fixed sides 21 face each other. The second axis extends parallel to the direction in which the two fixed sides 21 extend.

In this embodiment, the arrangement of the fixed portion at the edge has a symmetry of less than twice symmetry, and the axes of the first piezoelectric sheet and the second piezoelectric sheet whose axes of charge are large are orthogonal to each other. With such arrangement, the same effect as in the first embodiment can be obtained. This applies to all of the embodiments described below.
3. Third Embodiment A modification of the support substrate 1 will be described with reference to FIG. FIG. 9 is a plan view of a support substrate according to the third embodiment.

  As shown in FIG. 9, the support substrate 1B has an elliptical shape, and the entire edge is fixed to a housing (not shown) by an adhesive 8.

  The first and second piezoelectric sheets (not shown) are also elliptical.

By satisfying the condition that “the arrangement of the fixed portion of the edge portion has symmetry less than or equal to twice symmetry”, the first piezoelectric sheet and the second piezoelectric sheet (not shown) have support There is a first axis where a large tensile stress F1 is generated when bending together with the substrate 1B, and a second axis where a small tensile stress F2 is generated. The first axis extends parallel to the direction in which the elliptical minor axis extends. The second axis extends parallel to the direction in which the major axis of the ellipse extends.
4. Fourth Embodiment A modification of the support substrate 1 will be described with reference to FIG. FIG. 10 is a plan view of a support substrate according to the fourth embodiment.

  As shown in FIG. 8, the support substrate 1 </ b> C is rectangular, and only two opposing long sides 23 are fixed to the housing 6 by the adhesive 8.

  The first and second piezoelectric sheets (not shown) are also rectangular.

The first piezoelectric sheet and the second piezoelectric sheet (not shown) are provided with the support substrate 1 by satisfying the condition that “the arrangement of the fixed portion of the edge portion has symmetry of two-fold symmetry or less”. There is a first axis where a large tensile stress F1 is generated when bending together, and a second axis where a small tensile stress F2 is generated. The first axis extends parallel to the direction in which the two long sides 23 face each other. The second axis extends parallel to the direction in which the two long sides 23 extend.
5. Fifth Embodiment A modification of the support substrate 1 will be described with reference to FIG. FIG. 11 is a plan view of a support substrate according to the fifth embodiment.

  As shown in FIG. 11, the support substrate 1D is square, and two opposing first sides 25 are fixed to the housing 6 by a double-sided tape 8A, and two opposing second sides 27 are two-sided tapes 8B. Is fixed to the housing 6. Here, the double-sided tape 8A is harder than the double-sided tape 8B. That is, the double-sided tape 8A is made of a hard material, and the double-sided tape 8B is made of a soft material. That is, the first side 25 has higher rigidity than the second side 27. As described above, in this embodiment, the planar shape of the support substrate is four-fold symmetric, but the two-sided tape 8A having sufficiently high rigidity is formed on two sides, so that the first piezoelectric sheet and the second piezoelectric sheet have There is a first axis where a large tensile stress F1 generated when bending with the sheet member is generated, and a second axis where a small tensile stress F2 is generated. In other words, the condition that the arrangement of the fixed portion of the edge has symmetry of two-fold symmetry or less is satisfied.

  Therefore, even when the double-sided tape 8B having low rigidity is formed on the other two sides, the above condition is satisfied. In other words, the double-sided tape 8B needs to have such rigidity that the above conditions are satisfied.

  The first and second piezoelectric sheets (not shown) are also square.

The first axis extends parallel to the direction in which the second side 27 (double-sided tape 8B) having low rigidity extends. The second axis extends in parallel with the direction in which the two first sides 25 (double-sided tape 8A) having high rigidity extend.
6. Sixth Embodiment A modification of the support substrate 1 will be described with reference to FIG. FIG. 12 is a plan view of a support substrate according to the sixth embodiment.

  As shown in FIG. 12, the support substrate 1E is square, and two opposing first sides 25 are fixed to the housing 6 by a double-sided tape 8C, and two opposing second sides 27 are two-sided tapes 8D. Is fixed to the housing 6. Here, the line width of the double-sided tape 8C is larger than that of the double-sided tape 8D. As a result, the first side 25 has higher rigidity than the second side 27.

  As described above, since the double-sided tape 8C having sufficiently high rigidity is formed on two sides, the first piezoelectric sheet and the second piezoelectric sheet generate the first tensile stress F1 generated when bending together with the sheet member. There is an axis and a second axis where a small tensile stress F2 occurs. In other words, the condition that the arrangement of the fixed portion of the edge has symmetry of two-fold symmetry or less is satisfied.

Therefore, even when the double-sided tape 8D having low rigidity is formed on the other two sides, the above condition is satisfied. In other words, the double-sided tape 8D needs to have rigidity that satisfies the above conditions. The first piezoelectric sheet and the second piezoelectric sheet (not shown) are also square.

When the support substrate 1 satisfies the condition that the arrangement of the fixed portion at the edge has a symmetry of two-fold or less, the first piezoelectric sheet and the second piezoelectric sheet (not shown) There is a first axis where a large tensile stress F1 is generated when bending together with the support substrate 1E, and a second axis where a small tensile stress F2 is generated. The first axis extends in parallel to the direction in which the second side 27 (double-sided tape 8D) having low rigidity extends. The second axis extends in parallel with the direction in which the two first sides 25 (double-sided tape 8C) having high rigidity extend.
7. Seventh Embodiment The layer configuration of the device of the above embodiment is one embodiment, and the present invention is not limited to this. For example, the bimorph is of a serial type, but may be of a parallel type.

  Such an embodiment will be described with reference to FIG. FIG. 13 is a sectional view of the pressure detector of the seventh embodiment. Since the basic structure is the same as that of the above-described embodiment, the following description will focus on the differences.

  The pressure detector 100 mainly includes a support substrate 1, a piezoelectric sheet 3, and a detection electrode 4. As a basic operation of the pressure detector 100, when the support substrate 1 is pressed, the pressure detector 100 bends, a tensile stress is applied to the piezoelectric sheet 3, and an electric charge is generated. When the two detection electrodes 4 detect the charges, the pressing force applied to the pressure detector 100 can be detected.

  More specifically, the pressure detector 100 includes a support substrate 1, an adhesive layer 2, a first detection electrode 4c, a first piezoelectric sheet 3a, a second detection electrode 4d, and a second piezoelectric It has a sheet 3b and a third detection electrode 4e. Hereinafter, each configuration will be described.

  The piezoelectric sheet 3 is a sheet that generates a potential difference according to the pressing force applied to both surfaces when a bending force is applied. The piezoelectric sheet 3 has a first piezoelectric sheet 3a and a second piezoelectric sheet 3b. The first piezoelectric sheet 3a and the second piezoelectric sheet 3b are laminated so that the polarization directions are the same in the vertical direction.

  The detection electrode 4 includes a first detection electrode 4c, a second detection electrode 4d, and a third detection electrode 4e. The first detection electrode 4c is disposed between the support substrate 1 (specifically, the adhesive layer 2) and the first piezoelectric sheet 3a (that is, on the side of the first piezoelectric sheet 3a opposite to the second piezoelectric sheet 3b), The second detection electrode 4d is arranged between the first piezoelectric sheet 3a and the second piezoelectric sheet 3b. The third detection electrode 4e is arranged on the back side of the first piezoelectric sheet 3a (that is, on the side of the second piezoelectric sheet 3b opposite to the first piezoelectric sheet 3a).

  The first detection electrode 4c and the third detection electrode 4e are short-circuited to each other and connected to the ground. The second detection electrode 4d is connected to the detection circuit 53.

With the above-described circuit configuration, the detection circuit 53 determines the amount of electric charge generated in the first piezoelectric sheet 3a (positively large in this embodiment) and the amount of electric charge generated in the second piezoelectric sheet 3b (negative in this embodiment). (Small) can be obtained.
8. Other Embodiments A plurality of embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the invention. In particular, a plurality of embodiments and modifications described in this specification can be arbitrarily combined as needed.
(1) The planar shapes of the support substrate and the piezoelectric sheet are not limited to those of the above embodiment. For example, it may be a trapezoid, a parallelogram, or an irregular shape having a curve.
(2) The planar shapes of the support substrate and the piezoelectric sheet may be different from each other.
(3) In the above embodiments, the bimorph of the pressure detector was fixed to the support substrate 1, but the present invention is not limited to those embodiments. The bimorph of the pressure detector may be fixed to the back of the touch panel. In that case, not only the pressing force but also the pressing position can be detected. Examples of the touch panel include a capacitance type, a resistive type, and an optical type.

  INDUSTRIAL APPLICABILITY The present invention can be widely applied to a pressure detecting device, particularly to a pressure detecting device using a bimorph in which two piezoelectric sheets are bonded.

1: Support substrate 1a: Input surface 1b: Back surface 3: Piezoelectric sheet 3a: First piezoelectric sheet 3b: Second piezoelectric sheet 4: Detection electrode 4a: First detection electrode 4b: Second detection electrode 6: Housing 8: Adhesion Agent 100: pressure detector 110: electronic equipment

Claims (7)

An opening and a support portion surrounding the opening are provided so as to close the opening, and the pressure is detected using two piezoelectric sheets that generate electric charges by externally applied pressure. A pressure detector,
A sheet member having a first surface on which the pressure acts, and a second surface in which part or all of an edge portion is fixed and supported on the support portion by an adhesive layer;
An anisotropic first piezoelectric sheet that is arranged at the center of the second surface of the sheet member and that has an axis that is orthogonal to each other and has a large axis and a small axis that generate an amount of electric charge for elongation;
Anisotropically disposed opposite to the first piezoelectric sheet on the opposite side of the first piezoelectric sheet from the sheet member, and having an axis having a large axis and an axis having a small amount of electric charge generated with respect to elongation and being orthogonal to each other. And a second piezoelectric sheet of
The arrangement of the fixed portion of the edge has a symmetry of less than twice symmetry,
The first piezoelectric sheet and the second piezoelectric sheet are arranged such that the axes having the large charge amount are orthogonal to each other.
Pressure detector.   The pressure detecting device according to claim 1, wherein the fixed portion of the edge has a pair of first sides extending in a first direction.   The pressure detection device according to claim 2, wherein the pair of first sides are straight lines parallel to each other. 4. The pressure detection device according to claim 2, wherein the fixed portion of the edge is elongated in one direction in a plan view, and the pair of first sides are edges extending in a longitudinal direction. 5.   5. The pressure detection device according to claim 3, wherein the fixed portion of the edge has a pair of second sides connecting ends of the pair of first sides. 6.   The pressure detection device according to claim 5, wherein the second side has lower rigidity than the first side.   The pressure detecting device according to claim 2, wherein ends of the pair of first sides are arranged apart from each other and are discontinuous.

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